1. Field of the Invention
The present invention relates generally to mechanical presses and, in particular, to a shutheight adjustment mechanism utilizing a bolster hydraulic tie rod assembly to change press shutheight while the press is operating.
2. Description of the Related Art
Mechanical presses, for example, stamping presses and drawing presses, include a frame having a crown and bed with a slide supported within the frame for motion toward and away from the bed. The slide is driven by a crankshaft having a connecting arm connected to the slide. Such mechanical presses are widely used for stamping and drawing operations and vary substantially in size and available tonnage depending upon the intended use.
In prior art presses of this type, the slide is generally connected to the crankshaft by a connection mechanism rod which is adjustable in length. The connecting rod is attached to another member that is adjustable in its relation to the slide so that the shutheight opening between the slide and the bed can be adjusted to accommodate various die sets. A normal slide adjustment mechanism adjusts the slide to a predetermined operating shutheight. Alternatively, the bed portion or bolster of the press may have its position adjusted relative to the slide so as to adjust the shutheight therebetween, as disclosed in U.S. Pat. No. 3,858,432. Regardless of the mode of shutheight adjustment, the slide is generally guided on the uprights of the press frame extending between the crown and the bed so that the parts of the die set remain in precise registration as the slide reciprocates.
A prior art patent, U.S. Pat. No. 4,502,379, shows a press in which shutheight is controlled by adjustment members located between the press crown and bed. Expansion and contraction of the adjustment members was accomplished by supplying hydraulic fluid into the members and thereby changing shutheight.
Another example of press shutheight control is described in U.S. Pat. No. 4,939,918, in which a fluid chamber beneath the lower press die is filled with pressurized oil to cause changes in press shutheight or load.
In mechanical presses utilized in stamping staked laminations, for example, there is a need to maintain shutheight tolerances to within 0.001 to 0.002 inches. Staked laminations are normally utilized in construction of the stator or rotor cores of electric motors. These laminations need precisely stamped surfaces to allow the laminations to be press fit together. Control of press shutheight is also necessary to maintain accurate part tolerances and prolong die life. A particular problem with punch presses is that the press shutheight normally varies with changes in press speed and thermal changes in the press itself.
The present invention is directed to fill the needs and overcome the aforementioned problems associated with mechanical press shutheight adjustment mechanisms wherein it is desired to accurately control shutheight while the press is in operation by controlling the connecting force on the press tie rods.
The present invention provides an adaptable feedback shutheight system capable of automatically changing the shutheight to compensate for various press conditions.
Generally the invention provides a bolster hydraulic tie rod nut assembly connected to a feedback system that automatically changes press shutheight to compensate for various press changes. The hydraulic tie rod nut is constructed to vary the connecting force between the bolster and the bed applied therebetween in response to changes in an applied hydraulic fluid. While monitoring the press shutheight, the feedback control system changes the pressure communicated to the expandable tie rod nut assemblies, thereby changing the amount of compression between the bed and bolster combination and ultimately press shutheight. Crown movement can be effected in a similar fashion (as set forth in U.S. Pat. 5,285,722 and incorporated by reference herein), permitting yet a further mode of controlling press shutheight.
An advantage of the hydraulic tie rod assembly is that by incorporating the tie rod nut assembly with the monitoring of the shutheight, a feedback system is created to automatically change the hydraulic pressure to the tie rod nut assemblies.
Another advantage of the present invention is that the tie rod nut assembly with its associated feedback system can maintain the press shutheight to within 0.001 inches to 0.002 inches under changing press operating conditions. Further, press shutheight is dynamically controlled while the press is cycling.
An additional advantage of the shutheight adjustment apparatus of the present invention is that the tie rod assembly may be installed easily without any major changes to the press slide drive system.
A further advantage of the shutheight hydraulic tie rod assembly system is that it is possible to retrofit existing presses with the new system for more accurate shutheight adjustment and control.
An even further advantage of the tie rod assembly, being mounted to couple the bed and bolster together, is that the hydraulic tie rod nut assembly, whether mounted adjacent the bed or the bolster, is in an accessible yet generally protected position within the machine press.
A further advantage associated with having a plurality hydraulic tie rod nut assemblies associated with the bolster and bed is that, due to their relative proximity to the press shutheight region, the plurality of hydraulic tie nut assemblies can be more readily used to adjust for variances in shutheight that may occur across the width of the press.
Yet another advantage of the present invention is that it is still possible to preload the press. Preloading the press structure eliminates clearances between press parts, thereby making the press more dimensionally stable.
The invention, in one form thereof, comprises a press in which a crown and bed are attached together by a frame. A slide is attached to the crown for reciprocating movement in opposed relationship to a bolster mounted upon the bed. A plurality of tie rods connect between the bolster and the bed onto which are attached a plurality of pressure-activated tie rod nut assemblies associated with the bed and bolster, so that when activated, the nut assemblies can be used to force the bolster and bed toward one another in order to increase shutheight. A feedback means is connected to a shutheight measuring means and to the tie rod nut assemblies for comparing a predetermined desired shutheight to a measured shutheight. The feedback means activates the tie rod nut assemblies when the measured shutheight deviates from the predetermined shutheight.
A pressure-activated tie rod nut assembly includes a cylinder block having a cylinder bore fit about a tie rod. A piston is threadedly engaged about the tie rod and slidingly disposed within the cylinder bore thereby forming an inner chamber. A tie rod nut is threadably engaged about the tie rod, engaging the piston, so that when the inner chamber is pressurized with a fluid or liquid, the increase in pressure forces the piston and tie rod nut away from the cylinder block, thereby effectively forcing the bed and bolster together.